Field of the Invention
The present invention relates to an insert sleeve for fixing a screw in an object which is particularly of a soft material.
Description of the Prior Art
In the case of the fixing of parts on objects of a soft material, such as aluminium, plastics material, etc., difficulties are frequently encountered when the parts must be mounted and removed frequently. Indeed, these operations rapidly result in a deterioration of the screwthreads of the tapped holes formed in the object of a soft material, above all when the fixing screws are of a relatively hard material such as steel. It is already known to place in tapped holes formed in objects, assembly sleeves which are screwed in these tapped holes and serve as an intermediate part, interposed between the object of a soft material with which it is rendered rigid and the fixing screw which may be removed or remounted as many times as is desired without deteriorating in any way the screwthread of the tapped hole of this object. Further, it would be desirable that the sleeve itself be also replaceable, since it is of course also subject to wear when the mounting and removal occur very frequently.
French patent No. 1 308 201 describes a sleeve comprising a screwthread adapted to that of a tapped hole of the object, an inner screwthread adapted to a screw or other like member, and, at one of its ends, a cylindrical extension which is devoid of screwthreads and has an outside diameter which is equal to, or less than, the minor diameter of the outer screwthread of the sleeve.
When this sleeve is mounted in the object, the extension devoid of screwthreads is urged outwardly against the inner wall of the hole by a tool or punch which bears against an annular radial shoulder formed inside the extension. The force exerted by the tool then causes an upsetting or flow of the metal of the extension which, in deforming the entrance of the hole, is supposed to become intimately connected to the metal of the object. The deformation of the metal both of the extension and of the entrance of the hole thus corresponds to a flow, the deformation being progressive and following the progression of the tool. This sleeve of the prior art has in particular the following drawbacks.
As the metal of the extension is urged radially outwardly by a punch, the inside diameter of the extension must satisfy close tolerances so that the manufacture of the sleeve is expensive. The same is true in respect of the outside diameter which must be very precisely adapted to the diameter of the entrance of the hole formed in the object.
Moreover, owing to the flow of the metal of the extension and of the wall of the hole at the entrance of the latter, there is created not only a radial but also an axial locking, the bead formed externally on the extension preventing any subsequent removal of the sleeve. The latter consequently cannot be replaced. Other prior patents such as French patents No. 1 506 720, 1 416 714 and 2 400 139, disclose sleeves which have either or both of the aforementioned drawbacks.